1. Field of the Invention
The present invention relates to a technique for detecting an angular rate change of a supercharger and controlling an engine so as to prevent the supercharger from entering into a surging area in an electronically-controlled injected engine equipped with the supercharger.
2. Related Art
In an engine, as a mass of air inhaled therein is increased, a burning fuel can be enhanced so as to upgrade the power. A supercharger is a device that compresses ambient air, so as to increment the density of the air, and conducts it into a cylinder. For example, a turbocharger is well-known as a supercharger that rotates a turbine by the energy of discharged air and supercharges it with a compressor.
In an engine equipped with a supercharger, charging pressure is restricted by a surging area, regardless of whether the supercharger is a normal one or a variable geometry turbocharger (VGT). Surging is a phenomenon that generates a vibration as well as fluctuates air volume, wind pressure and rotation speed, and what is worse, causes an impossibility of traveling when the supercharger is driven in a state of connecting a centrifugal/axial flow blower or a compressor or the like to a conduit line so as to compressively squeeze the air volume.
The surging area is present in a high-speed rotation/low air capacity area where it is represented by a pressure curve with pressure and air volume as characteristics of the supercharger. This surging area boundary is referred to as a surging limitation. The surging limitation depends on the pressure level, the design of an impeller or the model of the supercharger and the like.
When the supercharger is driven beyond the surging limitation, an abnormal sound is generated due to the fluctuation of a boost pressure or a pressure wave vibration, which eventually leads to damages due to the vibration of the compressor. In general, since engines have dispersions of performance as products, an engine injection quantity is controlled so that the supercharger is driven in the area from the surging limitation to a slippage (allowance). Due to the necessity of the slippage for the engine, an advancement in a low speed torque was significantly limited.
Conventionally, there is a well-known method for limiting the injection quantity using a charging pressure sensor and the like when the supercharger is trapped in the surging state. However, this method can limit the injection quantity only when the surging is actually generated. In other words, the fact remains that the surging is actually generated and an abrasive inspiratory sound and a supercharger vibration are generated. There is a problem in terms of the credibility of this method.
For example, in JP 2003-240788, a means for measuring the pressure fluctuation of the supercharger and a turbo rotation number by a turbo rotation number sensor so as to control the supercharger is disclosed. However, the means according to JP 2003-240788, which detects only the turbo rotation number, can reduce the slippage based on the rotation number generated by the surging, but cannot completely eliminate it. Also, when an overspin characteristic of the turbo is generated during the transition duration, such as during the EGR blocking or the acceleration and deceleration, the turbo rotation number is mistakenly decided or the injection quantity is rapidly increased and decreased. Thus, there still remains a problem on the practical side.
Further, the turbo rotation number sensor as described in JP 2003-240788, which receives a signal from a shaft, can measure only one signal per one rotation. In this regard, the sensor cannot detect the turbo surging involving a rotation fluctuation. Moreover, in the turbo rotation number sensor as described in JP 2003-240788, a high peaking capacity is defined as the rotation number determined by performing a frequency analysis, in consideration of the case when the signal includes a noise. Accordingly, the sensor results in performing a filtering and cannot detect an instantaneous rotation fluctuation.
In other words, because the prior art and the turbo rotation number sensor as described in JP 2003-240788 cannot detect the limiting point of the turbo surging, the engine and the supercharger cannot be efficiently driven due to the need for slippage.
The problem to be solved is to identify the surging limitation so as to efficiently drive the engine.